1. Field of the Invention
The present invention relates to a phase control switching system which controls the switching timing of a power switching device for suppressing exciting rush currents or make-and-break surge voltages severe to system equipment such as a transformer, a reactor and a capacitor bank, or which controls the arcing time (arcing time period) of a circuit breaker to place the circuit breaker into a breaking or interrupting condition for the arcing time leading to no-re-ignition or for the optimal breaking time.
2. Description of the Related Art
In the recent years, there has been a tendency to more frequently use a switching apparatus equipped with an opening and closing (break-and-make) phase control system which suppresses the exciting rush current or switching surge voltage developing at the make or introduction by controlling the switching timing of a power switching device, or which cuts off the power to be supplied from a power bus to a load by controlling the arcing time of a circuit breaker for operating the circuit breaker at the arcing time for no-re-ignition or at the optimal breaking time.
FIGS. 13A and 13B are illustrations of configurations of a conventional circuit breaker opening phase control system disclosed in Japanese Unexamined Patent Publication No. 6-20564. Further, FIG. 14 shows reference (or standard) voltage waveforms at an opening operation of the conventional system and current waveforms in three phases: an R phase, an S phase and a T phase.
In FIG. 13A, a shunt reactor 91 is connected through a circuit breaker 2 to a power bus 5. Further a main section (body) 4 of the circuit breaker opening phase control system includes a reference phase detecting section 41 and control sections 42R, 42S and 42T for R, S and T phases on the power bus 5. A system voltage supplied from the power bus 5 is transformed through an input converter 73 into a voltage necessary for the processing in the interior of the circuit breaker opening phase control system 4, and then inputted to the reference phase detecting section 41.
Now, a description will be given hereinbelow of an operation of the conventional system.
The system voltage inputted from the power bus 5 through a meter transformer 3 is transformed through the input converter 73 into a voltage needed for the processing in the interior of the circuit breaker opening phase control system 4, and then inputted to the reference phase detecting section 41. The reference phase detecting section 41, when an opening command,is given to the circuit breaker 2, detects the voltage zero point of a reference phase voltage as shown in FIG. 14, thereby setting a periodic voltage zero point which produces a reference.
Furthermore, the point of time (time point) delayed by 1/4 cycle with respect to the voltage is set as a periodic current zero point. Simultaneously, the reference phase detecting section 41 outputs a signal to the respective phase control sections 42R, 42S, 42T, each of which calculates an opening operation time (CB opening time) in each of the R, S and T phases from the point of time of the opening command to the circuit breaker 2 to the point of time of CB opening start.
Subsequently, the reference phase detecting section 41 calculates an operating synchronization time (control time) so that the current zero occurs after the elapse of a predetermined arcing time (the time from the CB opening time to the final breaking time) at which each of the R, S and T phases provides the no-re-ignition.
In this case, a desired current zero point (breaking point) is set which is estimated after the elapse of a breaking time comprising a predetermined arcing time (2) plus an opening operation (CB opening) time (1) from a reference voltage zero point. Following this, calculated is an operating synchronization time (control time) ((3)+(4)) obtained by subtracting the breaking time ((1)+(2)) from a finish time ((1)+(2)+(3)+(4)) which is from the reference voltage zero point to the desired current zero point, where (3) designates a phase difference of a current of each phase flowing in a shunt reactor from an input voltage (R phase voltage) (90.degree. for the R phase, 210.degree. for the S phase and 330.degree. for the T phase). Further, symbol (4) denotes a correction time needed for the final breaking point to reach the current zero point of each phase.
In addition, the reference phase detecting section 41 outputs a control operation command for the circuit breaker 2 to the control section 42 for the corresponding phase after the elapse of the operating synchronization time from the reference voltage zero point, thus starting the operation of the circuit breaker 2.
The circuit breaker 2, starting its operation in response to this control, makes the separation of its contacts after the elapse of the opening operation time, and the final breaking point occurs in terms of each of the R, S and T phases after the predetermined arcing time (2). If this opening method is applied to a closing phase control system, since control to break at the point of time the insulation distance between the contacts of the circuit breaker 2 is sufficiently securable in each phase becomes feasible, the re-ignition becomes hard to generate.
FIG. 13B shows the addition of an averaged period measuring section 44 to the circuit breaker opening phase control system 4 shown in FIG. 13A. The other arrangement is the same as that of FIG. 13A. A single phase voltage input (V) is inputted through an input converter 43 to the averaged period measuring section 44. The averaged period measuring section 44 measures the time corresponding to each cycle of the input voltage to obtain an average period from the times obtained by measuring several times. Further, the averaged period measuring section 44 outputs a signal equivalent to the average period (a signal by which the zero point of the input voltage is found, such as a sine wave or a square wave). The following operation is identical to that of the system shown in FIG. 13A.
FIG. 15 illustratively shows a current waveform to be taken for when a conventional circuit breaker opening phase control system detects a current zero point and implements the opening phase control, and the timings for operations and the times.
A stand-by time plus an operating motive time correspond to a control time, an operation time corresponds to a CB opening operation, a contact separation time point corresponds to a CB opening start point, and a desired breaking point corresponds to a final breaking point.
Furthermore, FIG. 16 shows an operational sequence of the circuit breaker opening phase control system taking this breaking operation.
When the circuit breaker 2 receives an opening command, the reference phase detecting section 41 takes a system current to be broken from a meter current transformer CT in the interior of the current measuring section 71 to measure the current zero time point, thereafter calculating a current zero time point Tai in each phase.
At the same time, the opening and closing control section 42 for each phase receives an ambient temperature Temp of an operating mechanism from a temperature measuring section 51, an operating pressure or spring operating force Edrive from an operating force measuring section 52 and a control voltage Vcontrol from a control voltage measuring section 53 in a control room to calculate an operation time Topen given in advance as a function of these. Further, an arcing time Tarc is previously set to a predetermined time.
Following this, on the basis of the calculated current zero time point Tai, a reference (standard) point Tstandard of the opening operation start is set from a current zero point estimated to appear at the point of time of the occurrence of an opening command for the circuit breaker 2. Subsequently, a desired breaking point Ttarget is set from a current zero point estimated in like manner. At this time, an operating synchronization time Tconst is calculated according to an equation (Ttarget-Tstandard-Topen+Tarc) so that a breaking point occurs at a predetermined arcing time tarc. Further, a control opening command is outputted to the circuit breaker 2 at an operation starting time point Topen after the elapse of the operating synchronization time Tcont from the reference point Tstandard so that the opening operation of the circuit breaker 2 starts.
In consequence, a contact separation time point Tseparate is reached at the point of time of the elapse of the operation time Topen, and the opening is completed when a desired breaking point Tinterrupt after the elapse of the arcing time tarc.
However, in the case where the voltage and current zero points are taken as references through the use of the conventional system, the reference point can be taken only at every 0.5 cycle (every 10 ms in a 50-Hz system, every 8.3 ms in a 60-Hz system). For this reason, difficulty is experienced in using it for short-circuit fault current breaking control in which a reference time is required to be set for a shorter time and with higher accuracy.
In addition, in the case where the short-circuit fault current involves a direct-current component, particularly in the case where the direct-current component is in a large quantity, since a periodic current zero point does not occur, which creates a problem in that, if employing the method taken in the conventional system, it is impossible to set a current zero point to be used as a reference or standard.
Meanwhile, in the circuit breaker, the internal inspection for replacing expendable parts has been made when they reach a predetermined number of times of use, such as the frequency of short-circuit fault current interruption, the frequency of reactor bank switching and the frequency of capacitor bank switching. In the recent years, for the requirements on maintenance cost reduction to reach satisfaction, there is a need for a technique to diagnose the satisfactory quality of, particularly, contacts or insulating nozzles which form replaceable parts. However, the conventional system does not have a function to check the quality or health of the circuit breaker, so the maintenance and inspection take time.